This invention relates to the art of polybenzazole (PBZ) polymers and processes for synthesizing them.
Polybenzazole polymers are a known class of polymers comprising polybenzoxazole (PBO), polybenzothiazole (PBT), polybenzimidazole (PBI) and copolymers of these polymers. Polybenzazoles are generally classified as AB-polymers, containing a plurality of mer units depicted in formula 1(a), or AA/BB, containing a plurality of mer units which conform with formula 1(b) ##STR1## wherein:
each Ar is an aromatic group,
DM is a divalent organic moiety which is stable and inert under polymerization conditions, and
each Z is independently an oxygen atom, a sulfur atom, or a nitrogen atom that is bonded to a hydrogen atom or an organic moiety which is stable and inert in acid under polymerization conditions.
(For the purpose of this application, when the nitrogen atoms and Z moieties of a mer unit are depicted as bonded to an aromatic group without indicating their position, as in Formulae 1(a)-(b), it shall be understood that:
(1) each nitrogen atom and Z group within a given azole ring are bonded to the aromatic group in ortho position with respect to each other; and PA0 (2) if the mer unit has two azole rings, one nitrogen atom and Z moiety may be in either cis position or trans position with respect to the other nitrogen atom and Z moiety, for example illustrated in 11 Ency. Poly. Sci. & Eng., Polybenzothiazoles and Polybenzoxazoles, at 602 (J. Wiley & Sons 1988), which is incorporated herein by reference. The same understandings apply with respect to amine groups and Z moieties in a BB-PBZ monomer.) PA0 (1) contacting an AA-PBZ monomer with a selected molar excess of BB-PBZ monomer in a dehydrating solvent acid under conditions such that the monomers react to form polybenzazole oligomer: PA0 (2) maintaining the solution containing solvent acid and polybenzazole oligomer that results from step (1) under conditions such that the oligomers remain reactive to form higher molecular weight polymers: PA0 (3) contacting the solution resulting from step (2) with a selected amount of AA-PBZ monomer under conditions such that the polybenzazole oligomers and AA-PBZ monomer react to form polybenzazole polymers. PA0 (1) contacting a selected amount of AA-PBZ monomer with a selected amount of BB-PBZ monomer in a dehydrating solvent acid under conditions such that a mixture containing a polybenzazole oligomer is formed: PA0 (2) contacting a portion of the mixture resulting from Step (1) with a selected amount of chain extender and/or chain terminator in a continuous reactor with a residence time of no more than about one hour under conditions such that a dope containing higher molecular weight polybenzazole polymers is formed: PA0 (3) measuring a property of the dope and/or polymer resulting from step (2): and PA0 (4) adjusting the selected amount of chain extender and/or chain terminator added to the remaining portions of the mixture in step (2) to obtain a dope and/or polymer in which the measured property meets a selected value.
AA/BB-Polybenzazoles are synthesized by the reaction of at least one AA-PBZ monomer containing two electron-deficient carbon groups with at least one BB-PBZ monomer containing two o-amino-basic moieties. The reaction is illustrated generally in Formula 2: ##STR2## wherein each Q is an electron-deficient carbon group and all other moieties have the meaning and preferred embodiments previously given. The divalent organic moiety DM of the AA-monomer ordinarily comprises an aromatic group, which is most usually a p-phenylene group. The reaction is ordinarily carried out under non-oxidizing conditions in a non-oxidizing, dehydrating solvent acid, which is most frequently polyphosphoric acid.
Free base BB-PBZ monomers are susceptible to air oxidation. The monomers are typically handled and stored as hydrogen halide salts, because the salt is more stable with respect to oxidation.
The volatile hydrogen halide protecting acid is displaced by the solvent acid when the monomer is placed in solution. Afterwards, the volatile acid can interfere with the polymerization. Therefore, the volatile protective acid is ordinarily removed from the reaction solution in a devolatilization step before commencing polymerization. Devolatilization is frequently carried out at moderate temperatures (45.degree. C. to 100.degree. C.) in a polyphosphoric acid solution having a relatively low P.sub.2 O.sub.5 content (76 to 80 weight percent). The polymerization is carried out after devolatilization, at higher temperatures (150 to 220) in a solution having a higher P.sub.2 O.sub.5 content (80 to 90 weight percent), which is achieved by adding P.sub.2 O.sub.5 to the reaction mixture after the devolatilization step.
Polybenzazole polymers, their properties and their synthesis are discussed in detail in the following references: Sybert et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,772,678 (Sep. 20, 1988): Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,703,103 (Oct. 27, 1987): Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,533,692 (Aug. 6, 1985): Wolfe et al., Liquid Crystalline Poly(2,6-Benzothiazole) Compositions, Process and Products, U.S. Pat. No. 4,533,724 (Aug. 6, 1985): Wolfe, Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,533,693 (Aug. 6, 1985): Imai et al. "Polybenzoxazoles and Polybenzothiazoles," 83 Makromol. Chem. 167 (1965), Evers, Thermooxadatively Stable Articulated p-Benzobisoxazole and p-Benzobisthiazole Polymers, U.S. Pat. No. 4,359,567 (Nov. 16, 1982): Tsai et al., Method for Making Heterocyclic Block Copolymer, U.S. Pat. No. 4,578,432 (Mar. 25, 1986) and 11 Ency. Poly. Sci. & Eng., Polybenzothiazoles and Polybenzoxazoles, 601 (J. Wiley & Sons 1988), which are incorporated herein by reference.
The dopes resulting from polymerization are typically spun and drawn to form fibers by a dry-jet, wet spin process. Effective fiber spinning demands that the dope have very uniform and consistent properties, such as viscosity, both within each polymerization run and from one run to the other. The polymerization of polybenzazole contains many variables that can cause small changes in polymer and/or dope properties which are sufficient to affect the fiber quality. A method is needed to obtain a dope having consistent and reproducible properties.
The dehydrohalogenation of the reaction mixture is a particularly time consuming part of the polymerization process. It would be desirable to store dehydrohalogenated reaction mixtures for long periods of time until they are needed.